Hello, and welcome to the third part of our Soundproofing Series! Last time, we went over a few soundproofing tips that help you eliminate or reduce noise in your studio without having to spend a single cent. Check it out here if you haven’t already: Soundproofing Series #2 : Tips That Won’t Cost You A Cent
This time out, we’re going to go over some of the most important aspects of barriers, absorbers, and sealants. All of these are essential for reducing sound coming in and out of your studio. So if you are looking to go beyond the tips provided in the previous installment, the information here will be of interest to you.
So, without further ado…let’s jump right in!
Barriers, absorbers, and sealants…oh, my!
Let’s assume that you’ve already tried auditory masking, the inverse-square law, and carefully-placed mics (using the most appropriate polar patterns for the situation) at this point. If all these methods haven’t reduced problem noises enough, your next step is to use a combination of barriers, absorbers, and sealants.
How do these work?
Barriers essentially deflect sound waves, while absorbers…well, absorb them. Sealants‒especially caulks that are formulated to not harden, shrink, or crack over time‒ prevent airborne sound pressure waves from leaking in and out through the tiny gaps in the room construction.
All these solutions work on a basic principle: vibrations lose strength when passing through objects. By using the right combination of materials, vibrations and their resulting sound waves can be controlled quite well.
There are charts, lists, and graphs online that show the reflective and absorptive characteristics of various materials. The absorption amount of a particular material at various frequencies is referred to as the “absorption coefficient”.
Barriers, absorbers, and sealants all have specific capabilities and limitations. Unfortunately, there is a lot of misinformation about these solutions out there. Far too often, people spend a lot of money on the wrong type of acoustic treatment for the noise problem they are trying to solve.
Let’s take a look at two specific solutions that I know will do work wonders for reducing sound leakage based on my experience: gobos and absorbers.
Gobos range from big wooden or fiberglass walls that roll around on casters to something as simple as a few moving blankets. They can be pretty effective regardless of size.
Here’s a video I discovered after a quick search for acoustic gobo examples. It’s an instructor at the SAE institute in Miami, Florida showing the various DIY gobos they built for their studio.
That’s just one random example. There are lots of other ways you could easily and inexpensively make some to fit your own needs. But if you’d rather purchase something, those options are out there too. Here’s an example of a purpose built gobo sold by a retailer, designed specifically for isolating vocal recordings.
Although it probably isn’t practical for the long term, I’ve often pulled mattresses and the blankets off beds and used them as gobos when recording at home. By placing them between a mic and a sound I needed to attenuate, I could reduce unwanted noise to a considerable degree.
I’ve also used this method when recording two musicians playing in the same room simultaneously when I needed to reduce the amount of mic bleed between them. Or, between a mic and a really loud computer that was bleeding into the mic.
Admittedly, mattresses are VERY low on the visual “cool” scale in a studio environment. But they can be pretty effective when you don’t have any other options and you can’t argue with the results. Plus, you probably already own one or more, so you won’t have to spend money on additional soundproofing solutions.
I’ve also draped moving blankets over mic stands to reduce the level of sound coming from instruments. This method worked particularly well for a large grand piano that was bleeding into the orchestra mics too much. With the help of a few creatively placed gobos, the inverse square law and auditory masking enabled me to produce tracks that were clean enough to produce a great mix. What little bleed that remained was simply utilized as complementary low level reverb/reflection.
So, before telling all your neighbors to shut things down, do a little experimenting with mic selection and placement and a few gobos and/or blankets. You may be surprised at how quiet your tracks are!
Absorption serves an important purpose in wall, ceiling and floor construction, and for treating reflections inside finished rooms. A common myth, though, is that absorptive materials such as carpet, acoustic foam or fabric-covered insulation can be placed on walls, floors, or ceilings to stop sound from passing through into other rooms.
But while these may look cool and help control reflections bouncing around in the room, installing acoustic foam on the walls WILL NOT prevent sound from passing through. What will control sound transmission is a combination of mass and air space. To put it simply, foam, carpet, or insulation does not have the necessary mass to prevent sound from passing through a wall.
That covers the basics of soundproofing a room using barriers, absorbers, and sealants. Make sure to check out the next installment in the Soundproofing Series #3: Advanced Structural Solutions You Can Try.
– Alexander E. Jenkins